1. Field of the Invention
The invention relates to the methods for producing false color images. The invention also relates to apparatuses applying the said methods for producing false color images.
2. Description of the Related Art
Semiconductor video cameras include a number of semiconductor detectors, generally silicon-based detectors, which are arranged in line form or in matrix form. In addition, these detectors are generally coupled as CCD-detectors. Such CCD-detectors are sensitive for both visible light and near infrared radiation, as is illustrated in FIG. 1. In color video cameras based on semiconductors, there are generally two or three arrays of CCD-detectors, the first array whereof is used for detecting blue color B, and the second for detecting combined green G and red R, or alternatively only green color G, in which case red color R is detected by means of the third array. The spectrum ranges of different colors with respect to wavelength are illustrated in FIG. 1.
In ordinary video cameras, the access of near infrared radiation to the detectors is prevented by placing a filter cutting off near infrared radiation in front of the said detectors. The colors of the drawing, i.e. blue, green and red, are separated by means of another set of filters provided in front of the different detector arrays.
From the Finnish patent publication FI 79,641, there is known a method and apparatus for producing a false color image. In the invention described in the said patent publication, the false color image is created so that from two channels, i.e. detector arrays, the effect of near infrared radiation was electrically reduced, whereafter the signals R, G, B representing various colors were coded, and a video image resembling a false color image was created.
A drawback with the known method and apparatus is, that the video signal is electrically processed for several times, which weakens the image quality. Another drawback of the invention is that this kind of electrical arrangement for producing a false color image uses a relatively high amount of electric power, which is an obvious disadvantage for instance while surveying the surroundings with a false color camera from an aeroplane.